Sources for Large Plano-concave Lens? DiY Project

[basspig]

I've looked at the cost of wide angle add-on lenses for projectors and decided that was way over the limit of reasonable cost, so I'm seeking out a DiY solution to making a wide angle lens system, as an alternative to one of the expensive commercial lenses.

I have an InFocus IN82 projector, and am at the limit of distance, about 13' from the screen, as it would be blocked by a support column in the middle of the room if I go back farther, and also the bottom of the projected image would be too low and would pose a problem for seating in the front row.

I have a 6" plano-convex lens, but it bends light the wrong way, making the projected image much smaller. I need the reverse.

I perused the Edmund Scientific catalog and most everything they sell is only 25.4mm. I need abotu 75-100mm diameter, so I can mount it external to the projector and cover the entire beam. It looks like a relatively mild plano-concave lens would do the job, but I can't seem to locate one.

I know there are folks DiYing their own anamorphic lenses by using anything from award plaques made of glass to gluing glass panels together in a triangle and filling with vegetable oil.

Making a precision lens would probably be too much, but as I sit here looking at this 6" piece of glass on my desk, I know there are lenses made, somewhere, which are large enough to do the job.

I wonder how many here have pondered this very matter. Have you found a less expensive DiY solution? If so, where did you buy the raw lenses?

 

[BMXTRIX]

While I have not tried DIY solutions, I wonder why anyone would want to harm their image in such a way, or complain about the cost of doing so.

For a good photograph, it is the lens and the film. For a good projected image, it is the source, the processing, the imaging chip (LCD/DLP), then the optics.

One of the biggest problems many manufacturers had when they went to 1080p was the original optics which were designed for 720p were not good enough to maintain the quality and resolution for 1080p projection. They had to go through a fairly expensive recalibration and design process to get good 1080p optics and they are able to push that cost over thousands and thousands of projectors sold throughout the year.

IMO, there is no chance of a good DIY solution. The DIY solution is to be a professional optics manufacturer with access to top shelf grinding and polishing gear so you can put together the exact optics used by Schneider and other lens manufacturers that put these things together for projectors in the first place. Or, you are going to significantly impact the quality that your 1080p projector was designed to put out.

Yeah, I think that the expensive optics you end up buying from many manufacturers is more than people may need to spend. But, I'm not an optics manufacturer and I don't know what all really is necessary to maximize light transmission while keeping pincusioning and distortion in any manner to a minimum.

All I do know, is that ANYTHING put in the path of your projected image will bring the quality down, which is what I would work much harder to try to avoid than looking for the cheapest solution for a problem.

I do wish you luck and hopefully you will write about your endeavors and help others learn some things, especially if you do have success in them.

 

[basspig]

The quality issue is a great concern, and I forgot to mention that, however, milder amounts of light bending introduce milder amounts of error (eg. chromatic aberration, barrel distortion, etc.) I am acutely aware of these issues, being a cinematographer by profession. However, I also look to have the highest quality at the lowest cost, through a careful combination of purchasing methods and DIY. Ie., why spend $350,000 on stereo equipment when I can build a better set of speakers for under $38,000 and enjoy the benefits? I'm applying the same to my DIY theater construction. I saved $5,650 by building my own AT screen, and saved over a thousand on velvet drapes by sewing my own from raw fabrics. The projector, I got on eBay for 26cents on the dollar. Naturally, I'm resistant to spending more on the lens than I did for the projector.